1. Field of the Invention
The present invention relates to a scan method of a capacitive touch device, and especially relates to a clustered scan method of a capacitive touch device.
2. Description of the Related Art
Currently capacitive touch devices usually have two types of scan methods, namely, self-capacitance scanning method and mutual-capacitance scanning method. Various types of mutual-capacitance scanning methods have been developed and dedicated for different demands of capacitive touch devices. Clustered scan method is one of the mutual-capacitance scanning methods. Several examples of the clustered scan method are described as follows.
As disclosed in U.S. Pat. No. 7,812,827, a simultaneous sensing arrangement technique is applied to a capacitive touch device having multiple sensing points intersected by drive lines and sense lines. Such technique can enhance operation of multi-touch sensing configuration by simultaneously driving multiple rows of the drive lines of the capacitive touch device. With reference to FIG. 4A, given 16 drive lines X0-X15 as an example, the drive lines can be classified into four groups, that is, groups 1-4. Each group includes four drive lines. With reference to FIG. 4B, according to the clustered scan method disclosed by said US patent, two driving signals 801, 802 are simultaneously output to the drive lines in the groups 1 and 2, and sensed values are represented by X0, X1. As the two driving signals have four in-phase pulses heading in a time duration T1 and four pulses mutually phase-shifted by a 180-degree trailing in a time duration T2, the sensed values in the time durations T1 and T2 can be considered as (X0+X1) and (X0−X1) respectively.
Likewise, after two driving signals 806, 807 are applied to the drive lines in groups 3 and 4 in time durations T3 and T4, sensed values (X2+X3) and (X2−X3) are respectively obtained. By sending driving signals to all the drive lines of each non-overlapped group and varying phases of the driving signals, finger touch can be preliminarily determined by a combined result of the sensed values X0-X3.
Another clustered scan method is disclosed by US Patent Publication No. 2013/0271410 and applied to an integrated type of liquid crystal display (LCD) touch display of a capacitive touch device. The clustered scan method primarily uses driving signals with different frequencies to scan first, and then determines a noise value under each driving signal. The lower the noise value is, the fewer noise a corresponding driving signal has. Those driving signals with relatively low noise will be used to perform scanning.
With reference to FIG. 5, in steps 4 to 19, a vertical blank interval (VBI) of an LCD display device is used for scanning fifteen drive lines. Three driving signals with different frequencies A to C are applied to the fifteen drive lines in steps 4 to 7. The driving signal with the frequency A is simultaneously applied to the drive lines indicated by R0, R4, R8 and R12. The driving signal with the frequency B is simultaneously applied to the drive lines indicated by R1, R5, R9 and R13. The driving signal with the frequency C is simultaneously applied to the drive lines indicated by R3, R7, R11 and R14. The rest of the drive lines are not driven.
In steps 8 to 11, the foregoing three driving signals are simultaneously applied to the subsequent drive lines next to the drive lines previously driven in steps 4 to 7. In other words, the driving signal with frequency A is simultaneously applied to the drive lines indicated by R1, R5, R9 and R13, the driving signal with frequency B is simultaneously applied to the drive lines indicated by R2, R6, R10 and R14, the driving signal with frequency C is simultaneously applied to the drive lines indicated by R4, R8 and R12, and the rest of the drive lines are not driven. The three driving signals are repeatedly applied in a similar fashion until the scanning process from steps 4 to 11 can be carried out four times. During each scanning process, the phases of the frequencies A, B, C of the driving signals can be further changed and marked by -A, -B and -C. Hence, the use of driving signals with different frequencies and phases can increase the scanning speed and provide better signal-to-noise ratio (SNR).
To cope with the issue of unsatisfactory SNR, US Patent Publication No. 2013/0057480 discloses a technique pertinent to “signal-to-noise ratio in touch” to increase SNR and measurement accuracy of a signal generated by touch event or an approaching touch object. With reference to FIG. 6, the technique involves simultaneous application of driving signals 410A, 410B to two drive lines X0, X1. Given four drive lines X0-X3 as an example, consecutive two of the drive lines (X0, X1), (X1, X2), (X2, X3) are sequentially driven. Suppose that the voltage level of the driving signals 410A-410G is identical to the voltage level of the driving signal that drives only one drive line, when two drive lines are driven at the same time, a sensing value of a corresponding sense line is doubled. Hence, the SNR increases. However, despite the disclosure of simultaneously driving two, three or four drive lines for the purpose of higher SNR, this technique fails to point out how bordering drive lines should be driven when multiple drive lines are simultaneously driven. For example, if there are n drive lines, when two drive lines are simultaneously driven, the sensing values of non-bordering drive lines, such as the second drive line to the (n−2)th drive line, may be as twice as the sensing value of the bordering sense line, such as the first sense line or the last sense line, and a false touch determination may occur.
From the foregoing examples of the clustered scan method, the clustered scan method is rather common to touch devices. Different clustered scan methods are addressed for corresponding touch devices and technical issues thereof to be resolved. However, none of the clustered scan methods points out how bordering drive lines should be driven.